This can be completely false and made up but I thought it was weird enough to report here. A DigitalPoint Forum thread named Mysterious GMail Image - Girl Sticking Out Tongue! shows a link to a comment at a particular blog, where a gmail user says his gmail logo was replaced by a picture of a woman. He posted a screen shot here of the gmail screen, with the woman replacing the logo.
This site also notes the image, saying;
Have You Seen This Person?
Many Gmail users have seen this image when checking their mail tonite. This journalist figures it must have been an inside job because Google has a whole team of security experts. The question is then, when will we know for sure?
I am not sure what exactly is up here, it can most likely be a hoax. Or perhaps Google getting ready for April Fools Day.
Forum discussion at DigitalPoint Forums.